U.S. patent application number 15/126503 was filed with the patent office on 2017-03-23 for embedded permanent magnet rotary electric machine.
This patent application is currently assigned to MITSUBISHI ELECTRIC CORPORATION. The applicant listed for this patent is MITSUBISHI ELECTRIC CORPORATION. Invention is credited to Ryuichi TAKIGUCHI, Toshinori TANAKA, Eigo TOTOKI.
Application Number | 20170085143 15/126503 |
Document ID | / |
Family ID | 54287625 |
Filed Date | 2017-03-23 |
United States Patent
Application |
20170085143 |
Kind Code |
A1 |
TANAKA; Toshinori ; et
al. |
March 23, 2017 |
EMBEDDED PERMANENT MAGNET ROTARY ELECTRIC MACHINE
Abstract
R1>R2>R3 is satisfied, where R1 is a radius of curvature
of a cylindrical surface that contacts circular arc-shaped curved
surfaces arranged circumferentially, R2 is a radius of curvature of
the circular arc-shaped curved surfaces, and R3 is a radius of
curvature of an upper surface of permanent magnets, air gaps are
formed on radially outer portions of two circumferential side
portions of magnet housing apertures, surfaces that contact two
circumferential side surfaces of the permanent magnets so as to be
parallel to a radial direction are disposed on radially inner
portions of the two circumferential end portions, and B2>B1 is
satisfied, where B1 is a thickness of a core portion of the rotor
core between the circular arc-shaped curved surfaces and the magnet
housing apertures at a magnetic pole center, and B2 is a thickness
of a circumferential end portion of the core portion.
Inventors: |
TANAKA; Toshinori;
(Chiyoda-ku, JP) ; TOTOKI; Eigo; (Chiyoda-ku,
JP) ; TAKIGUCHI; Ryuichi; (Chiyoda-ku, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MITSUBISHI ELECTRIC CORPORATION |
Chiyoda-ku |
|
JP |
|
|
Assignee: |
MITSUBISHI ELECTRIC
CORPORATION
Chiyoda-ku
JP
|
Family ID: |
54287625 |
Appl. No.: |
15/126503 |
Filed: |
February 24, 2015 |
PCT Filed: |
February 24, 2015 |
PCT NO: |
PCT/JP2015/055213 |
371 Date: |
September 15, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H02K 1/278 20130101;
H02K 29/03 20130101; H02K 1/2706 20130101; H02K 2201/03 20130101;
H02K 2213/03 20130101; H02K 1/276 20130101; H02K 1/146 20130101;
H02K 2201/06 20130101 |
International
Class: |
H02K 1/27 20060101
H02K001/27; H02K 1/14 20060101 H02K001/14 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 8, 2014 |
JP |
2014-079387 |
Claims
1-8. (canceled)
9: An embedded permanent magnet rotary electric machine comprising:
an annular stator; and a rotor that is disposed coaxially inside
said stator so as to have an air gap interposed, wherein: said
rotor comprises: a rotor core that has an external shape in which a
plurality of circular arc-shaped curved surfaces that are convex
radially outward are arranged circumferentially, and in which
magnet housing apertures are formed so as to pass axially through
an inner radial side of each of said circular arc-shaped curved
surfaces; a rotating shaft that is inserted into a central axial
position of said rotor core, and that holds said rotor core; and
permanent magnets that are each produced into a rod-shaped body in
which a radially outer side of a cross section that is
perpendicular to a longitudinal direction is a circular arc that is
convex radially outward, and in which two circumferential side
surfaces are flat surfaces that are parallel to a plane that
includes a magnetic pole center, said permanent magnets being
housed in each of said magnet housing apertures; R1>R2>R3 is
satisfied, where R1 is a radius of curvature of a cylindrical
surface that contacts said circular arc-shaped curved surfaces that
are arranged circumferentially, R2 is a radius of curvature of said
circular arc-shaped curved surfaces, and R3 is a radius of
curvature of an upper surface of said permanent magnets; said
magnet housing apertures comprise air gap portions in which
radially outer portions of two circumferential side portions are
expanded circumferentially outward; surfaces that are parallel to a
plane that includes said magnetic pole center that contact said two
circumferential side surfaces of said permanent magnets are
disposed on radially inner portions of said two circumferential
side portions of said magnet housing apertures; B2>B1 is
satisfied, where B1 is a thickness of a core portion of said rotor
core between said circular arc-shaped curved surfaces and said
magnet housing apertures at said magnetic pole center, and B2 is a
thickness of a circumferential end portion of said core portion;
and a distance between circumferentially adjacent air gap portions
and a distance between circumferentially adjacent surfaces among
said surfaces that are parallel to said plane that includes said
magnetic pole center that contact said two circumferential side
surfaces of said permanent magnets are equal.
10: The embedded permanent magnet rotary electric machine according
to claim 9, wherein Wm+0.05 mm.ltoreq.Ws.ltoreq.Wm+0.1 mm is
satisfied, where Wm is a circumferential width between radially
inner end portions of two circumferential side portions of said
permanent magnets, and Ws is a circumferential width between said
radially inner end portions of said two circumferential side
portions of said magnet housing apertures.
11: The embedded permanent magnet rotary electric machine according
to claim 9, wherein said permanent magnets are formed so as to have
a cross-sectional shape perpendicular to a longitudinal direction
in which a radially outer side is a circular arc that is convex
radially outward and a radially inner side is a circular arc that
is convex radially outward, R1>R4>R2>R3 being satisfied,
where R4 is a radius of curvature of a lower surface of said
permanent magnets.
12: The embedded permanent magnet rotary electric machine according
to claim 10, wherein said permanent magnets are formed so as to
have a cross-sectional shape perpendicular to a longitudinal
direction in which a radially outer side is a circular are that is
convex radially outward and a radially inner side is a circular arc
that is convex radially outward, R1>R4>R2>R3 being
satisfied, where R4 is a radius of curvature of a lower surface of
said permanent magnets.
13: The embedded permanent magnet rotary electric machine according
to claim 9, wherein a lower surface of said permanent magnets is
formed into a flat surface that is perpendicular to a direction of
a radius that passes through a circumferentially central portion of
said permanent magnets.
14: The embedded permanent magnet rotary electric machine according
to claim 10, wherein a lower surface of said permanent magnets is
formed into a flat surface that is perpendicular to a direction of
a radius that passes through a circumferentially central portion of
said permanent magnets.
15: The embedded permanent magnet rotary electric machine according
to claim 9, wherein a circumferential thickness of said rotor core
between magnet housing apertures that are adjacent to each other in
a circumferential direction is thicker than a radial thickness of
core portions of said rotor core on an outer circumferential side
of two circumferential side portions of said permanent magnets.
16: The embedded permanent magnet rotary electric machine according
to claim 10, wherein a circumferential thickness of said rotor core
between magnet housing apertures that are adjacent to each other in
a circumferential direction is thicker than a radial thickness of
core portions of said rotor core on an outer circumferential side
of two circumferential side portions of said permanent magnets.
17: The embedded permanent magnet rotary electric machine according
to claim 9, wherein said rotor core is configured such that n core
segments are arranged axially, where n is an integer that is
greater than or equal to two, and magnetic pole centers of core
segments that are axially adjacent are offset in a circumferential
direction.
18: The embedded permanent magnet rotary electric machine according
to claim 10, wherein said rotor core is configured such that n core
segments are arranged axially, where n is an integer that is
greater than or equal to two, and magnetic pole centers of core
segments that are axially adjacent are offset in a circumferential
direction.
19: The embedded permanent magnet rotary electric machine according
to claim 17, wherein said embedded permanent magnet rotary electric
machine is a three-phase embedded permanent magnet motor, said
stator comprises: an annular back yoke; teeth each that protrude
radially inward from said back toke so as to be arranged; and a
stator winding that is mounted to slots that are formed by said
back yoke and adjacent teeth; a number of slots per phase per pole
is one half or one quarter; and an angle of offset in said
circumferential direction between said magnetic pole centers of
said core segments that are axially adjacent is greater than or
equal 30 electrical degrees and less than or equal 48 electrical
degrees.
20: The embedded permanent magnet rotary electric machine according
to claim 17, wherein a gap is disposed between said core segments
that are axially adjacent.
21: The embedded permanent magnet rotary electric machine according
to claim 19, wherein a gap is disposed between said core segments
that are axially adjacent.
22: The embedded permanent magnet rotary electric machine according
to claim 20, wherein B1.ltoreq.d is satisfied, where d is said
gap.
23: An embedded permanent magnet rotary electric machine
comprising: an annular stator, and a rotor that is disposed
coaxially inside said stator so as to have an air gap interposed,
wherein: said rotor comprises: a rotor core that has an external
shape in which a plurality of circular arc-shaped curved surfaces
that are convex radially outward are arranged circumferentially,
and in which magnet housing apertures are formed so as to pass
axially through an inner radial side of each of said circular
arc-shaped curved surfaces; a rotating shaft that is inserted into
a central axial position of said rotor core, and that holds said
rotor core; and permanent magnets that are each produced into a
rod-shaped body in which a radially outer side of a cross section
that is perpendicular to a longitudinal direction is a circular arc
that is convex radially outward, and in which two circumferential
side surfaces are flat surfaces that are parallel to a plane that
includes a magnetic pole center, said permanent magnets being
housed in each of said magnet housing apertures; R1>R2>R3 is
satisfied, where R1 is a radius of curvature of a cylindrical
surface that contacts said circular arc-shaped curved surfaces that
are arranged circumferentially, R2 is a radius of curvature of said
circular arc-shaped curved surfaces, and R3 is a radius of
curvature of an upper surface of said permanent magnets; said
magnet housing apertures comprise air gap portions in which
radially outer portions of two circumferential side portions are
expanded circumferentially outward; surfaces that are parallel to a
plane that includes said magnetic pole center that contact said two
circumferential side surfaces of said permanent magnets are
disposed on radially inner portions of said two circumferential
side portions of said magnet housing apertures; B2>B1 is
satisfied, where B1 is a thickness of a core portion of said rotor
core between said circular arc-shaped curved surfaces and said
magnet housing apertures at said magnetic pole center, and B2 is a
thickness of a circumferential end portion of said core portion;
end plates are disposed so as to contact two axial end surfaces of
said rotor core and so as to cover at least a portion of said
permanent magnets when viewed from an axial direction; and a radial
position of outer circumferential edges of said end plates is
greater than or equal to a radial position of a point that is half
of a thickness of said permanent magnets at said magnetic pole
center, and is less than or equal to a radial position of a point
of intersection between said upper surface and side surface of said
permanent magnets.
24: The embedded permanent magnet rotary electric machine according
to claim 23, wherein said rotor core is configured such that n core
segments are arranged axially, where n is an integer that is
greater than or equal to two, and magnetic pole centers of core
segments that are axially adjacent are offset in a circumferential
direction.
25: The embedded permanent magnet rotary electric machine according
to claim 24, wherein said embedded permanent magnet rotary electric
machine is a three-phase embedded permanent magnet motor, said
stator comprises: an annular back yoke; teeth each that protrude
radially inward from said back toke so as to be arranged; and a
stator winding that is mounted to slots that are formed by said
back yoke and adjacent teeth; a number of slots per phase per pole
is one half or one quarter; and an angle of offset in said
circumferential direction between said magnetic pole centers of
said core segments that are axially adjacent is greater than or
equal 30 electrical degrees and less than or equal 48 electrical
degrees.
26: The embedded permanent magnet rotary electric machine according
to claim 24, wherein a gap is disposed between said core segments
that are axially adjacent.
27: The embedded permanent magnet rotary electric machine according
to claim 25, wherein a gap is disposed between said core segments
that are axially adjacent.
28: The embedded permanent magnet rotary electric machine according
to claim 26, wherein B1.ltoreq.d is satisfied, where d is said gap.
Description
TECHNICAL FIELD
[0001] The present invention relates to an embedded permanent
magnet rotary electric machine that includes a rotor in which
permanent magnets are embedded in a rotor core.
BACKGROUND ART
[0002] In rotary electric machines such as industrial and vehicular
motors, there is demand for reductions in size, increases in speed,
and a widening of service speed ranges. Various embedded permanent
magnet rotary electric machines that include a rotor in which
permanent magnets are embedded in a rotor core have been proposed
as rotary electric machines to meet these demands (see Patent
Literature 1 and 2, for example).
CITATION LIST
Patent Literature
[0003] Patent Literature 1: Japanese Patent Laid-Open No.
2001-178037 (Gazette)
[0004] Patent Literature 2: Japanese Patent Laid-Open No. HEI
5-304737 (Gazette)
SUMMARY OF THE INVENTION
Problem to be Solved by the Invention
[0005] In a conventional embedded permanent magnet rotary electric
machine according to Patent Literature 1, because an outer
circumferential surface of a rotor core is a cylindrical surface,
many harmonics are present in the magnetomotive force waveforms
that are generated by the rotor, and one problem has been that
cogging torque and torque ripples arise. Because the outer
circumferential surface of the rotor core is a cylindrical surface,
the core portion of the rotor core that is subjected to q-axis
magnetic flux is in close proximity to a stator, increasing q-axis
inductance. Thus, voltage saturation is more likely to occur during
high-speed rotation, and another problem has been that the
operating range cannot be widened. In addition, because internal
shapes of magnet housing apertures and external shapes of the
magnets are similar shapes, from the viewpoint of dimensional
tolerances, the internal shapes of the magnet housing apertures are
larger than the external shapes of the magnets, and another problem
has been that gaps are more likely to arise between radially inner
end portions on two circumferential side portions of the magnets
and the magnet housing apertures in particular. Furthermore,
because the two circumferential side portions of the permanent
magnets are flat surfaces that are inclined relative to a magnetic
pole center, the thicknesses of the two circumferential side
portions of the permanent magnets are thinner parallel to the
magnetic pole center. Operating points of the two side portions of
the permanent magnets are thereby lower than an operating point of
a central portion of the permanent magnets, and another problem has
been that demagnetization of the magnets is more likely to
occur.
[0006] In a conventional embedded permanent magnet rotary electric
machine according to Patent Literature 2, an outer circumferential
surface of the rotor core that forms magnetic poles is configured
into a shape in which two ellipses are superimposed so as to be
perpendicular to each other to reduce harmonics that are present in
the magnetomotive force waveform that is generated by the rotor.
However, in the conventional embedded permanent magnet rotary
electric machines according to Patent Literature 2, because
internal shapes of magnet housing apertures and external shapes of
the magnets are also similar shapes, one problem has also been that
gaps are more likely to arise between radially inner end portions
on two circumferential side portions of the magnets and the magnet
housing apertures. Furthermore, because the two circumferential
side portions of the permanent magnets are flat surfaces that are
inclined relative to the magnetic pole center, the thicknesses of
the two circumferential side portions of the permanent magnets are
thinner parallel to the magnetic pole center. Operating points of
the two side portions of the permanent magnets are thereby lower
than an operating point of a central portion of the permanent
magnets, and one problem has been that demagnetization of the
magnets is more likely to occur.
[0007] The present invention aims to solve the above problems and
an object of the present invention is to provide an embedded
permanent magnet rotary electric machine that can reduce cogging
torque and torque ripples, that can expand an operating range, that
can fix magnets without disposing clearances in a rotor core, and
that can also suppress demagnetization of the magnets.
Means for Solving the Problem
[0008] An embedded permanent magnet rotary electric machine
according to the present invention includes: an annular stator; and
a rotor that is disposed coaxially inside the stator so as to have
an air gap interposed. The rotor includes: a rotor core that has an
external shape in which a plurality of circular arc-shaped curved
surfaces that are convex radially outward are arranged
circumferentially, and in which magnet housing apertures are formed
so as to pass axially through an inner radial side of each of the
circular arc-shaped curved surfaces; a rotating shaft that is
inserted into a central axial position of the rotor core, and that
holds the rotor core; and permanent magnets that are each produced
into a rod-shaped body in which a radially outer side of a cross
section that is perpendicular to a longitudinal direction is a
circular arc that is convex radially outward, and in which two
circumferential side surfaces are flat surfaces that are parallel
to a plane that includes a magnetic pole center, the permanent
magnets being housed in each of the magnet housing apertures.
R1>R2>R3 is satisfied, where R1 is a radius of curvature of a
cylindrical surface that contacts the circular arc-shaped curved
surfaces that are arranged circumferentially, R2 is a radius of
curvature of the circular arc-shaped curved surfaces, and R3 is a
radius of curvature of an upper surface of the permanent magnets,
the magnet housing apertures include air gap portions that are
formed by expanding radially outer portions of two circumferential
side portions circumferentially outward, surfaces that contact the
two circumferential side surfaces of the permanent magnets so as to
be parallel to a radial direction are disposed on radially inner
portions of the two circumferential side portions of the magnet
housing apertures, and B2>B1 is satisfied, where B1 is a
thickness of a core portion of the rotor core between the circular
arc-shaped curved surfaces and the magnet housing apertures at the
magnetic pole center, and B2 is a thickness of a circumferential
end portion of the core portion.
Effects of the Invention
[0009] According to the present invention, the rotor core is formed
so as to have an external shape that is configured by arranging
circumferentially a plurality of circular arc-shaped curved
surfaces 13 that are convex radially outward. Thus, harmonics that
are present in the magnetomotive force waveform that is generated
by the rotor are reduced, enabling the generation of cogging torque
and torque ripples to be suppressed. Because the portions of the
rotor core that are subjected to q-axis magnetic flux are separated
from the stator, q-axis inductance is reduced. Thus, voltage
saturation is less likely to occur during high-speed rotation,
enabling the operating range to be expanded.
[0010] Because R1>R2>R3 is satisfied, where R1 is a radius of
curvature of a cylindrical surface, R2 is a radius of curvature of
the circular arc-shaped curved surfaces, and R3 is a radius of
curvature of an upper surface of the permanent magnets, the
thicknesses of the core portions of the rotor core on a radially
outer side of the permanent magnets become gradually thicker away
from the magnetic pole centers. Thus, the core portions radially
outside the permanent magnets at the magnetic pole centers easily
become magnetically saturated, reducing the amount of magnetic
leakage flux in the magnet magnetic flux, thereby enabling
increased output to be achieved. In addition, because the amount of
magnetic flux that reaches the air gap from the permanent magnets
gradually reduces away from the magnetic pole centers, the harmonic
magnetic flux density component in the air gap magnetic flux
density component is reduced, enabling generation of cogging torque
and torque ripples to be suppressed.
[0011] Because the magnet housing apertures have air gap portions
that are formed by expanding radially outer portions of two
circumferential side portions circumferentially outward,
irregularities in the permanent magnets are absorbed by the air gap
portions when the permanent magnets are housed in the magnet
housing apertures. In addition, surfaces that are parallel to the
two circumferential side surfaces of the permanent magnets and the
radial direction, that are formed on radially inner portions of the
two circumferential side portions of the magnet housing apertures,
contact the two circumferential side surfaces of the permanent
magnets. The permanent magnets can thereby be fixed to the rotor
core without disposing clearances.
[0012] Because B2>B1 is satisfied, where B1 is a thickness of a
core portion of the rotor core between the circular arc-shaped
curved surfaces and the magnet housing apertures at a magnetic pole
center, and B2 is a thickness of a circumferential end portion of
the core portion, q-axis magnetic flux is less likely to flow
through the core portion. Thus, q-axis inductance is reduced in the
rotor, enabling the operating range to be expanded.
[0013] Because the two circumferential side portions of the
permanent magnets are formed into flat surfaces that are inclined
relative to the magnetic pole centers, the thickness of the two
circumferential side portions of the permanent magnets in a
direction that is parallel to the magnetic pole centers becomes
thicker, raising the operating points of the two side portions of
the permanent magnets, and enabling demagnetization of the
permanent magnets to be suppressed. In addition, because the
thickness in the regions of the rotor core that are positioned
radially outside the permanent magnets gradually becomes thicker
toward the two side portions from a circumferentially central
portion, magnetic flux from the stator is less likely to pass
through the two side portions of the permanent magnets, enabling
demagnetization of the permanent magnets to be suppressed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a cross section that shows an embedded permanent
magnet rotary electric machine according to Embodiment 1 of the
present invention;
[0015] FIG. 2 is a partial enlargement that shows a vicinity of a
permanent magnet of a rotor in the embedded permanent magnet rotary
electric machine according to Embodiment 1 of the present
invention;
[0016] FIG. 3 is a schematic diagram that explains flow of q-axis
magnetic flux in a rotor of the embedded permanent magnet rotary
electric machine according to Embodiment 1 of the present
invention;
[0017] FIG. 4 is a cross section that shows a rotor in a
comparative embedded permanent magnet rotary electric machine;
[0018] FIG. 5 is a partial enlargement that shows a vicinity of a
permanent magnet of a rotor core in the comparative embedded
permanent magnet rotary electric machine;
[0019] FIG. 6 is a schematic diagram that explains flow of q-axis
magnetic flux in the rotor of the comparative embedded permanent
magnet rotary electric machine;
[0020] FIG. 7 is a schematic diagram that shows pathways of q-axis
magnetic flux in the rotor of the embedded permanent magnet rotary
electric machine according to Embodiment 1 of the present
invention;
[0021] FIG. 8 is a cross section that shows the permanent magnet in
the embedded permanent magnet rotary electric machine according to
Embodiment 1 of the present invention;
[0022] FIG. 9 is a partial enlargement that shows a vicinity of a
magnet insertion aperture of a rotor core in the embedded permanent
magnet rotary electric machine according to Embodiment 1 of the
present invention;
[0023] FIG. 10 is a graph that shows magnitude of cogging torque
when an outer circumferential surface shape of the rotor core is
modified in the embedded permanent magnet rotary electric machine
according to Embodiment 1 of the present invention;
[0024] FIG. 11 is an end elevation that shows a rotor core in an
embedded permanent magnet rotary electric machine according to
Embodiment 2 of the present invention;
[0025] FIG. 12 is a partial enlargement that shows a vicinity of a
permanent magnet of a rotor in the embedded permanent magnet rotary
electric machine according to Embodiment 2 of the present
invention;
[0026] FIG. 13 is an end elevation that shows a rotor core in an
embedded permanent magnet rotary electric machine according to
Embodiment 3 of the present invention;
[0027] FIG. 14 is a cross section that shows the rotor core in the
embedded permanent magnet rotary electric machine according to
Embodiment 3 of the present invention;
[0028] FIG. 15 is a partial enlargement that shows a vicinity of a
permanent magnet of a rotor in the embedded permanent magnet rotary
electric machine according to Embodiment 3 of the present
invention;
[0029] FIG. 16 is a diagram that explains flow of magnetic leakage
flux in the rotor of the embedded permanent magnet rotary electric
machine according to Embodiment 3 of the present invention;
[0030] FIG. 17 is a partial enlargement that shows the vicinity of
the permanent magnet of the rotor in the embedded permanent magnet
rotary electric machine according to Embodiment 3 of the present
invention;
[0031] FIG. 18 is a cross section that shows an embedded permanent
magnet rotary electric machine according to Embodiment 4 of the
present invention;
[0032] FIG. 19 is an oblique projection that shows a rotor core in
the embedded permanent magnet rotary electric machine according to
Embodiment 4 of the present invention;
[0033] FIG. 20 is a graph that shows a relationship between torque
ripples and step skew angle in the embedded permanent magnet rotary
electric machine according to Embodiment 4 of the present
invention;
[0034] FIG. 21 is a side elevation that shows a rotor core in an
embedded permanent magnet rotary electric machine according to
Embodiment 5 of the present invention;
[0035] FIG. 22 is a side elevation that shows a rotor core in an
embedded permanent magnet rotary electric machine according to
Embodiment 6 of the present invention; and
[0036] FIG. 23 is a partial enlargement that shows a vicinity of a
permanent magnet of a rotor in an embedded permanent magnet rotary
electric machine according to Embodiment 7 of the present
invention.
DESCRIPTION OF EMBODIMENTS
[0037] Preferred embodiments of an embedded permanent magnet rotary
electric machine according to the present invention will now be
explained with reference to the drawings.
Embodiment 1
[0038] FIG. 1 is a cross section that shows an embedded permanent
magnet rotary electric machine according to Embodiment 1 of the
present invention, FIG. 2 is a partial enlargement that shows a
vicinity of a permanent magnet of a rotor in the embedded permanent
magnet rotary electric machine according to Embodiment 1 of the
present invention, FIG. 3 is a schematic diagram that explains flow
of q-axis magnetic flux in a rotor of the embedded permanent magnet
rotary electric machine according to Embodiment 1 of the present
invention, FIG. 4 is a cross section that shows a rotor in a
comparative embedded permanent magnet rotary electric machine, FIG.
5 is a partial enlargement that shows a vicinity of a permanent
magnet of a rotor core in the comparative embedded permanent magnet
rotary electric machine, FIG. 6 is a schematic diagram that
explains flow of q-axis magnetic flux in the rotor of the
comparative embedded permanent magnet rotary electric machine, FIG.
7 is a schematic diagram that shows pathways of q-axis magnetic
flux in the rotor of the embedded permanent magnet rotary electric
machine according to Embodiment 1 of the present invention, FIG. 8
is a cross section that shows the permanent magnet in the embedded
permanent magnet rotary electric machine according to Embodiment 1
of the present invention, and FIG. 9 is a partial enlargement that
shows a vicinity of a magnet insertion aperture of a rotor core in
the embedded permanent magnet rotary electric machine according to
Embodiment 1 of the present invention.
[0039] In FIG. 1, an embedded permanent magnet rotary electric
machine 100 includes: an annular stator 1; and a rotor 10 that is
coaxially and rotatably disposed inside the stator 1 so as to have
an air gap 9 interposed.
[0040] The stator 1 includes a stator core 2 that is produced by
stacking and integrating electromagnetic steel sheets, and that is
formed such that teeth 2b each protrude radially inward from an
inner wall surface of an annular back yoke 2a so as to be arranged
at a uniform angular pitch circumferentially. In this case, thirty
slots 2c that are formed by the back yoke 2a and adjacent teeth 2b
are arranged circumferentially. Furthermore, although not shown,
distributed winding stator windings are mounted to the stator core
2.
[0041] The rotor 10 includes: a rotor core 12 that is produced by
stacking and integrating electromagnetic steel sheets, and that has
an external shape in which a plurality of circular arc-shaped
curved surfaces 13 are arranged at a uniform angular pitch
circumferentially; a rotating shaft 11 that is inserted into and
fixed to a central axial position of the rotor core 12; and
permanent magnets 16 that are embedded into an outer
circumferential side of the rotor core.
[0042] As shown in FIG. 2, the rotor core 12 is configured such
that ten protruding portions that have a radius of curvature R2,
that are formed by the circular arc-shaped curved surfaces 13, are
arranged at a uniform angular pitch circumferentially. The ten
circular arc-shaped curved surfaces 13 that are arranged
circumferentially contact a cylindrical surface 14 that has a
radius of curvature R1. Magnet housing apertures 15 are formed so
as to pass axially through the rotor core 12 on an inner radial
side of each of the circular arc-shaped curved surfaces 13.
[0043] As shown in FIGS. 2 and 8, the permanent magnets 16 are
produced into rod-shaped bodies that have a length that is
approximately equal to an axial length of the rotor core 12, and in
which a cross-sectional shape that is perpendicular to a
longitudinal direction is formed so as to have a circular arc shape
that is surrounded by an upper side that is convex radially outward
that has a radius of curvature R3, a lower side that is convex
radially outward that has a radius of curvature R4, and a pair of
flanking sides that are formed by parallel straight lines. The
permanent magnets 16 are inserted into and fixed to the respective
magnet housing apertures 15, and are arranged circumferentially
such that polarities of surfaces (upper surfaces) on outer
circumferential sides of the permanent magnets 16 line up
alternately as a North-seeking (N) pole, a South-seeking (S) pole,
an N pole, an S pole, etc. Moreover, Wm is a spacing between the
pair of flanking sides of the permanent magnets 16, that is, a
circumferential width.
[0044] As shown in FIGS. 2 and 9, the magnet housing apertures 15
are formed so as to have an aperture shape that is a similar shape
to an external shape of the permanent magnets 16 except for having
air gap portions 17 that are formed by expanding radially outer
portions of two circumferential side portions circumferentially
outward. Moreover, Ws is a spacing between magnet detent portions
18 (described below), that is, a circumferential width.
[0045] Here, in the cross section that is perpendicular to a
central axis of the rotating shaft 11, the radius of curvature R1
of the cylindrical surface 14 is greater than the radius of
curvature R4 of the lower surfaces of the permanent magnets 16,
which is greater than the radius of curvature R2 of the circular
arc-shaped curved surfaces 13, which is greater than the radius of
curvature R3 of the upper surfaces of the permanent magnets 16.
Moreover, radii of curvature of the upper surface and the lower
surface of the inner wall surfaces of the magnet housing apertures
15 approximately match the radius of curvature R3 of the upper
surfaces of the permanent magnets 16 and the radius of curvature R4
of the lower surfaces of the permanent magnets 16, respectively.
The circular arc-shaped curved surfaces 13, the aperture shapes of
the magnet housing apertures 15, and the external shapes of the
permanent magnets 16 each have mirror symmetry that has a plane
that passes through the central axis of the rotating shaft 11 and a
circumferential center of the circular arc-shaped curved surfaces
13 as a plane of symmetry. This plane of symmetry is a magnetic
pole center.
[0046] The core portions of the rotor core 12 on a radially outer
side of the permanent magnets 16 constitute bridge portions 20.
These bridge portions 20 are formed such that thickness becomes
thicker circumferentially away from the magnetic pole centers. The
thickness at the magnetic pole center of the bridge portions 20 is
B1, and the thickness of the circumferential end portions is B2
(>B1).
[0047] Interpolar centers are planes that pass through the central
axis of the rotating shaft 11 and centers between circumferentially
adjacent magnet housing apertures 15 (permanent magnets 16). The
facing wall surfaces of the air gap portions 17 of the
circumferentially adjacent magnet housing apertures 15 are parallel
to the interpolar centers. Radially inner portions of the two
circumferential side portions of the magnet housing apertures 15,
i.e., the radially inner portions of the air gap portions 17, are
wall surfaces that are parallel to the magnetic pole centers, and
form magnet detent portions 18. Lb is a distance between the
circumferentially adjacent air gap portions 17, and Ln is a
distance between the circumferentially adjacent magnet detent
portions 18.
[0048] The embedded permanent magnet rotary electric machine 100
that is configured in this manner operates as a ten-pole
thirty-slot rotary electric machine.
[0049] According to Embodiment 1, the outer circumferential surface
of the rotor core 12 is configured such that ten circular
arc-shaped curved surfaces 13 that have a radius of curvature R2
are arranged at a uniform angular pitch circumferentially. Thus,
the harmonics that are present in the magnetomotive force waveform
that is generated by the rotor 10 are reduced compared to Patent
Literature 1, which uses a rotor that has a perfectly circular
external shape, enabling the generation of cogging torque and
torque ripples to be suppressed. Because the portions of the rotor
core 12 that are subjected to q-axis magnetic flux are separated
from the stator 1, q-axis inductance is reduced. Thus, voltage
saturation is less likely to occur during high-speed rotation,
enabling the operating range to be expanded.
[0050] Because the aperture shape of the magnet housing apertures
15 is formed so as to have a similar shape to the permanent magnets
16 except for having air gap portions 17 that are formed by
expanding radially outer portions of two circumferential side
portions circumferentially outward, dimensional irregularities in
the permanent magnets 16 are absorbed by the air gap portions 17,
when the permanent magnets 16 are housed in the magnet housing
apertures 15. The magnet detent portions 18 that are constituted by
the radially inner sides of the two circumferential side portions
of the magnet housing apertures 15 contact the two circumferential
side surfaces of the permanent magnets 16 so as to be parallel
thereto in a radial direction, enabling the permanent magnets 16 to
be fixed without disposing clearances in the rotor core 12. By
fixing the permanent magnets 16 in this manner without disposing
clearances in the rotor core 12, the magnet positions cease to be
irregular. Thus, it becomes possible to suppress cogging torque and
torque ripples that occur due to irregularities in magnet
position.
[0051] Because the two circumferential side portions of the
permanent magnets 16 are flat surfaces that are parallel to the
magnetic pole centers, the operating points of the two side
portions of the permanent magnets 16 are higher because the magnet
thicknesses of the two side portions of the permanent magnets 16 in
the direction that is parallel to the magnetic pole centers is
thicker, suppressing demagnetization of the permanent magnets
16.
[0052] Because the air gap portions 17 are formed integrally in the
two circumferential side portions of the magnet housing apertures
15, the width Lb of the interpolar core portions is narrower. Thus,
magnetic leakage flux is reduced in the magnet magnetic flux due to
magnetic saturation of the core portions in question, enabling
output to be improved.
[0053] Now, a rotary electric machine in which a rotor core 12 was
used that has an outer circumferential surface that is configured
by arranging ten circular arc-shaped curved surfaces 13 that have a
radius of curvature R2 at a uniform angular pitch circumferentially
(R1>R2>R3) and a rotary electric machine in which a rotor
core was used that has a perfect circle as an external shape
(R1=R2>R3) were prepared, and cogging torque was measured, the
results thereof being shown in FIG. 10. FIG. 10 is a graph that
shows magnitude of cogging torque when an outer circumferential
surface shape of the rotor core is modified in the embedded
permanent magnet rotary electric machine according to Embodiment 1
of the present invention. Moreover, the rotor core that has a
perfect circle as an external shape is configured in a similar
manner to the rotor core 12 except that it has a cylindrical
surface that contacts the circular arc-shaped curved surfaces 13 of
the rotor core 12 as an outer circumferential surface. Furthermore,
in FIG. 10, the magnitude of the cogging torque of the rotary
electric machine that used a rotor core that has a perfect circle
as an external shape (R1=R2>R1) is shown when the magnitude of
the cogging torque of the rotary electric machine that used the
rotor core 12 (R1>R2>R3) is one.
[0054] From FIG. 10, it was confirmed that cogging torque is
significantly reduced when a rotor core 12 is used that has an
outer circumferential surface that is configured by arranging
circular arc-shaped curved surfaces 13 that have a radius of
curvature R2 at a uniform angular pitch circumferentially compared
to when a rotary electric machine in which a rotor core is used
that has a perfect circle as an external shape (R1=R2>R3) were
prepared, and cogging torque was measured, the results thereof
being shown in FIG. 10. This cogging torque-reducing effect can be
inferred to be due to the harmonics that are present in the
magnetomotive force waveform that is generated by the rotor being
reduced when a rotor core 12 that has an outer circumferential
surface that is configured by arranging circular arc-shaped curved
surfaces 13 that have a radius of curvature R2 at a uniform angular
pitch circumferentially is used compared to when a rotor core that
has a perfect circle as an external shape is used.
[0055] Next, effects due to the radius of curvature R3 of the outer
circumferential surfaces of the permanent magnets 16 being smaller
than the radius of curvature R2 of the circular arc-shaped curved
surfaces 13 will be explained in contrast to a comparative
example.
[0056] As shown in FIGS. 4 and 5, a rotor 110 in a comparative
embedded permanent magnet rotary electric machine is configured in
a similar manner to the rotor 10 in the present embedded permanent
magnet rotary electric machine 100 except that the radius of
curvature R1 of the cylindrical surface 14 of the rotor core 112 is
greater than the radius of curvature R2 of the circular arc-shaped
curved surfaces 13, which is equal to the radius of curvature R3 of
the upper surfaces of the permanent magnets 16, in a cross section
that is perpendicular to a central axis of the rotating shaft 11.
Because the radius of curvature R2 of the circular arc-shaped
curved surfaces 13 in the comparative rotor 110 is equal to the
radius of curvature R3 of the upper surfaces of the permanent
magnets 16, the thickness of the bridge portions 20 is uniform. In
other words, the thickness B1 at the magnetic pole centers of the
bridge portions 20 and the thickness B2 at the two circumferential
end portions of the bridge portions 20 are equal.
[0057] In the comparative rotor 110, the mechanical strength of the
bridge portions 20 is reduced if the thickness B2 of the two end
portions of the bridge portions 20 is reduced, and there is a
possibility that the bridge portions 20 may be damaged due to
centrifugal forces that act on the permanent magnets 16 during
high-speed rotation. The q-axis magnetic flux that the stator
winding produces enters the two circumferential end portions of the
bridge portions 20. Because the thickness B2 of the two end
portions of the bridge portions 20 is thinner, the q-axis magnetic
flux passes through the bridge portions 20, and flows through the
permanent magnets 16 on a radially inner side, as indicated by the
arrows in FIG. 6. Here, the q-axis magnetic flux flows through the
permanent magnets 16 in an opposite direction to the direction of
orientation of magnetization, and the permanent magnets 16 are
subjected to a demagnetizing field, facilitating demagnetization of
the permanent magnets 16.
[0058] Furthermore, in the comparative the rotor 110, the
mechanical strength of the bridge portions 20 could be increased
and demagnetization of the permanent magnets 16 by the q-axis
magnetic flux could be suppressed by increasing the thickness B2 at
the two end portions of the bridge portions 20. However, increasing
the thickness B2 at the two end portions of the bridge portions 20
would increase the thickness B1 of the bridge portions 20 at the
magnetic pole centers, increasing the magnetic leakage flux in the
magnet magnetic flux. Thus, increases in torque due to the magnetic
flux that is generated by the permanent magnets 16 would be
suppressed, reducing output.
[0059] In the rotor 10 of the present embedded permanent magnet
rotary electric machine 100, because the radius of curvature R3 of
the outer circumferential surface of the permanent magnets 16 is
smaller than the radius of curvature R2 of the circular arc-shaped
curved surfaces 13, the thickness B1 of the bridge portions 20 at
the magnetic pole centers is formed so as to be thinner than the
thickness B2 at the two circumferential end portions. Thus, because
magnetic leakage flux in the magnet magnetic flux is reduced by
magnetic saturation at the magnetic pole centers of the bridge
portions 20, torque due to the magnetic flux that is generated by
the permanent magnets 16 is increased, enabling output to be
improved. Furthermore, because the thickness B2 at the two
circumferential end portions of the bridge portions 20 can be
increased, the mechanical strength of the bridge portions 20 is
high, enabling centrifugal force resistance to be increased. In
addition, the thickness of the bridge portions 20 becomes thicker
circumferentially away from the magnetic pole centers. Thus, the
amount of magnetic flux that exits the permanent magnets 16 and
reaches the air gap 9 decreases from the magnetic pole centers
toward the interpolar sides. The harmonic magnetic flux density
component in the air gap magnetic flux density component is reduced
thereby, reducing cogging torque and torque ripples.
[0060] Because the thickness B2 at the two circumferential end
portions of the bridge portions 20 is increased, the q-axis
magnetic flux that the stator winding produces flows from the two
circumferential end portions of the bridge portions 20 radially
inward through interpolar core portions, as indicated by arrows in
FIG. 3. Thus, the demagnetizing field that acts on the permanent
magnets 16 due to the q-axis magnetic flux flowing through the
permanent magnets 16 is reduced, suppressing demagnetization of the
permanent magnets 16.
[0061] Because the radius of curvature R4 of the lower surface of
the permanent magnets 16 is greater than the radius of curvature R3
of the upper surface of the permanent magnets 16, magnet volume is
reduced away from the magnetic pole centers. Thus, the amount of
magnetic flux that exits the permanent magnets 16 and reaches the
air gap 9 decreases from the magnetic pole centers toward the
sides. The harmonic magnetic flux density component in the air gap
magnetic flux density component is reduced thereby, reducing the
cogging torque and torque ripples.
[0062] Next, as indicated by the arrows in FIG. 7, the q-axis
magnetic flux that has entered the rotor core 12 takes: a pathway
in which it flows radially through the interpolar core portion,
flows circumferentially through a core portion on the radially
inner side of the permanent magnets 16, and flows radially outward
through the neighboring interpolar core portion; and a pathway in
which it flows circumferentially through the bridge portions
20.
[0063] The thickness B2 of the two end portions of the bridge
portions 20 is determined by structural constraints. Thus, if an
identical amount of magnet is used, the thicknesses B2 of the two
end portions of the bridge portions 20 of the rotor 10 of the
present embedded permanent magnet rotary electric machine 100 and
the rotor 110 of the comparative embedded permanent magnet rotary
electric machine are identical. In the present rotor 10, because B1
is less than B2, the q-axis magnetic flux is less likely to flow
through the bridge portions 20 compared to the comparative rotor
110. Because of that, the q-axis inductance in the rotor 10 is less
than in the comparative rotor 110.
[0064] Now, the voltage when the embedded permanent magnet rotary
electric machine 100 operates as a motor is expressed by Expression
(1). Here, V0 is the voltage, R is winding resistance of the stator
winding, Lp is q-axis inductance, Ld is d-axis inductance, Iq is
q-axis electric current, Id is d-axis electric current, and .PHI.f
is permanent magnet density.
[FORMULA 1]
V.sub.0= {square root over
(RId-.omega.LqIq).sup.3+(RIq+.omega.(LdId+.phi.f)).sup.2)}
Expression (1)
[0065] It can be seen from Expression (1) that voltage V0 decreases
as Lp decreases. This means that voltage saturation of the motor is
superior. Because the q-axis inductance Lq is reduced, as mentioned
above, it can be seen that the operating range of the present
embedded permanent magnet rotary electric machine 100 can be
expanded compared to the comparative embedded permanent magnet
rotary electric machine.
[0066] There are also manufacturing constraints on Ln, B1, and B2,
in addition to structural constraints. The rotor core 12 is formed
by laminating and integrating electromagnetic steel sheets that
have been punched out. If the sheet thickness of the
electromagnetic steel sheets is t, then the width of Ln, B1, and B2
that can be produced by punching is a width that is greater than or
equal to 0.4.times.t. Thus, if there are no problems with the
structural strength, it is ideal to punch the electromagnetic steel
sheets such that B1 is equal to 0.4.times.t. Magnetic leakage flux
in the magnet magnetic flux can be reduced thereby, increasing
torque due to the magnet magnetic flux, and enabling output to be
improved.
[0067] However, if the electromagnetic steel sheets are punched
such that B1 is equal to 0.4.times.t using a die, then it is
necessary to punch in a plurality of increments so that the bridge
portions 20 do not bend. Because of that, the die is larger, and
punching machine time is increased, increasing costs. For this
reason, it is desirable to make B1 greater than or equal to
1.4.times.t in order not to increase the size of the die, and to
suppress increases in punching machine time. From the viewpoint of
reducing the magnetic leakage flux in the magnet magnetic flux, it
is particularly desirable to make B1 equal to 1.4.times.t.
[0068] Next, the aperture shape of the magnet housing apertures 15
and the external shape of the permanent magnets 16 will be
investigated. Making the circumferential width Wm of the permanent
magnets 16 equal to the circumferential width Ws between the magnet
detent portions 18 of the magnet housing apertures 15 leads to
increased magnet volume. The amount of magnetic flux that is
generated by the permanent magnets 16 is increased thereby,
enabling output to be improved.
[0069] Considering dimensional tolerances during manufacturing, it
is desirable to set Ws so as to satisfy Wm+0.05
mm.ltoreq.Ws.ltoreq.Wm+0.1 mm. If Ws is set to equal Wm+0.1 mm in
particular, then the circumferential width Wm of the permanent
magnets 16 can be maximized.
[0070] In addition, if the distance Lb between the facing air gap
portions 17 and the distance Ln between the facing magnet detent
portions 18 are made equal, then the circumferential width Wm of
the permanent magnets 16 can be maximized while ensuring the
mechanical strength of the bridge portions 20, enabling output to
be improved.
[0071] Moreover, in Embodiment 1 above, the stator winding is
constituted by distributed windings, but the stator winding is not
limited to distributed windings, and concentrated windings may be
used.
[0072] In Embodiment 1 above, a ten-pole thirty-slot rotary
electric machine has been explained, but the number of poles and
the number of slots in the rotary electric machine are not limited
thereto.
[0073] In Embodiment 1 above, the radius of curvature R4 of the
lower surface of the permanent magnets is greater than the radius
of curvature R3 of the upper surface, but the radius of curvature
R4 of the lower surface of the permanent magnets may be less than
or equal to the radius of curvature R3 of the upper surface.
Embodiment 2
[0074] FIG. 11 is an end elevation that shows a rotor core in an
embedded permanent magnet rotary electric machine according to
Embodiment 2 of the present invention, and FIG. 12 is a partial
enlargement that shows a vicinity of a permanent magnet of a rotor
in the embedded permanent magnet rotary electric machine according
to Embodiment 2 of the present invention.
[0075] In FIGS. 11 and 12, a rotor 10A includes: a rotor core 12A
that has an external shape in which a plurality of circular
arc-shaped curved surfaces 13 are arranged at a uniform angular
pitch circumferentially, and in which magnet housing apertures 15A
are formed on an inner radial side of each of the circular
arc-shaped curved surfaces 13; and permanent magnets 16A that are
inserted into and fixed to each of the magnet housing apertures
15A.
[0076] The permanent magnets 16 are produced into rod-shaped bodies
that have a length that is approximately equal to an axial length
of the rotor core 12, and in which a cross-sectional shape that is
perpendicular to a longitudinal direction is formed so as to have a
semicylindrical shape that is surrounded by an upper side that has
a radius of curvature R3, a lower side that is formed by straight
line that is perpendicular to a direction of a radius that passes
through a circumferential center of the upper side, and a pair of
flanking sides that are formed by straight lines that are parallel
to the direction of the radius that passes through the
circumferential center of the upper side.
[0077] As shown in FIGS. 2 and 9, the magnet housing apertures 15A
are formed so as to have an aperture shape that is a similar shape
to an external shape of the permanent magnets 16A except for having
air gap portions 17 that are formed by expanding radially outer
portions of two circumferential side portions circumferentially
outward.
[0078] Moreover, the rest of the configuration is formed in a
similar or identical manner to that of Embodiment 1 above.
[0079] Consequently, similar or identical effects to those of
Embodiment 1 above can also be achieved in Embodiment 2.
[0080] According to Embodiment 2, because the permanent magnets 16A
are produced into rod-shaped bodies that have a semicylindrical
cross section, machining of the permanent magnets 16A is
facilitated compared to the permanent magnets 16 in which the upper
and lower surfaces were formed into circular arc-shaped curved
surfaces, enabling cost reductions to be achieved.
[0081] Because the lower surfaces of the permanent magnets 16A are
formed into flat surfaces that are perpendicular to the magnetic
pole centers, magnet volume is reduced away from the magnetic pole
centers. Thus, the amount of magnetic flux that exits the permanent
magnets 16A and reaches the air gap 9 decreases from the magnetic
pole centers toward the interpolar sides. The harmonic magnetic
flux density component in the air gap magnetic flux density
component is reduced thereby, reducing the cogging torque and
torque ripples.
Embodiment 3
[0082] FIG. 13 is an end elevation that shows a rotor core in an
embedded permanent magnet rotary electric machine according to
Embodiment 3 of the present invention, FIG. 14 is a cross section
that shows the rotor core in the embedded permanent magnet rotary
electric machine according to Embodiment 3 of the present
invention, FIG. 15 is a partial enlargement that shows a vicinity
of a permanent magnet of a rotor in the embedded permanent magnet
rotary electric machine according to Embodiment 3 of the present
invention, FIG. 16 is a diagram that explains flow of magnetic
leakage flux in the rotor of the embedded permanent magnet rotary
electric machine according to Embodiment 3 of the present
invention, and FIG. 17 is a partial enlargement that shows the
vicinity of the permanent magnet of the rotor in the embedded
permanent magnet rotary electric machine according to Embodiment 3
of the present invention.
[0083] In FIGS. 13 through 15, a rotor 10B is fixed to a rotating
shaft 11 by shrinkage fitting or press-fitting, etc., and includes
end plates 21 that are disposed so as to contact two axial end
surfaces of a rotor core 12. The end plates 21 are produced into
ring-shaped flat plates that have a diameter Rm at which outer
circumferential edges thereof are level with radial positions of
points of intersection between upper surfaces and side surfaces of
the permanent magnets 16.
[0084] Moreover, the rest of the configuration is formed in a
similar or identical manner to that of Embodiment 1 above.
[0085] In Embodiment 3, because the rotor core 12, the magnet
housing apertures 15, and the permanent magnets 16 are also
configured in a similar or identical manner to those of Embodiment
1 above, similar effects to those in Embodiment 1 above can be
achieved.
[0086] In Embodiment 3, the end plates 21 are fixed to the rotating
shaft 11 so as to be in contact with the two axial end surfaces of
the rotor core 12 so as to overlap with at least a portion of the
permanent magnets 16 when viewed from an axial direction. Thus,
even if there are electromagnetic imbalances, and thrust acts
axially on the permanent magnets 16, axial movement of the
permanent magnets 16 is prevented by the end plates 21.
Consequently, axial dislodgment of the permanent magnets 16 from
the rotor core 12 is reliably prevented.
[0087] Now, from a viewpoint of suppressing leakage of magnetic
flux that emerges from the permanent magnets 16, it is desirable to
produce the end plates 21 using a nonmagnetic material. However, if
end plates 21 that are produced using a nonmagnetic material are
fixed to the rotating shaft 11 by shrinkage fitting or
press-fitting, etc., then there is a possibility that the joined
portions between the end plates 21 and the rotating shaft 11 may
loosen as the temperature of the rotor 10B increases due to
differences in thermal expansion coefficient between the end plates
21 and the rotating shaft 11, and the end plates 21 may dislodge.
If the interfitting tolerance is made too strict in order to
prevent loosening of the joined portions between the end plates 21
and the rotating shaft 11, it becomes necessary to raise the
shrinkage fitting temperature in the shrinkage fitting step, and
insertion pressure rises in the press-fitting step, degrading
workability. From the above, it is desirable for the end plates 21
to be produced using a magnetic material.
[0088] If the diameter Rm of end plates 21 that are produced using
a magnetic material is equal to the outside diameter of the rotor
core 12, then the entire end surface of the permanent magnets 16 is
in contact with the end plates 21, increasing the magnetic leakage
flux. Here, the area of the end surfaces of the permanent magnets
16 that contact the end plates 21 can be reduced by reducing the
diameter Rm of the end plates 21. As indicated by the arrows in
FIG. 16, the magnetic flux that emerges from the permanent magnets
16 thereby enters the end plates 21 from regions of the end
surfaces of the permanent magnets 16 that contact the end plates
21, flows radially inward through the end plates 21, then enters a
core portion of the rotor core 12 on the radially inner side of the
permanent magnets 16, and flows through magnetic paths that return
to the permanent magnets 16. Thus, because the flow of magnetic
flux from the regions of the end surfaces of the permanent magnets
16 that are exposed from the end plates 21 toward the end plates 21
is suppressed, magnetic leakage flux can be reduced compared to
when the outside diameter of the end plates 21 is made equal to the
outside diameter of the rotor core 12. Thus, the smaller the area
of the end plates 21 that contacts the end surface of the permanent
magnets 16, the more magnetic leakage flux can be reduced.
[0089] Furthermore, if the end plates 21 cover even a portion of
the permanent magnets 16 when viewed from an axial direction, they
are effective in suppressing axial dislodgment of the permanent
magnets 16. As shown in FIG. 17, in order to reliably stop axial
dislodgment of the permanent magnets 16, it is sufficient if the
end plates 21 cover a region that is greater than or equal to half
of a thickness Hm of the permanent magnets 16 at the magnetic pole
center when viewed from the axial direction.
[0090] From the above, it is desirable to set the outside diameter
Rm such that the radial position of the outer circumferential edges
of the end plates 21 is greater than or equal to a radial position
of a point that is half of the thickness Hm of the permanent
magnets 16 at the magnetic pole center, and is less than or equal
to a radial position of a point of intersection between the upper
surface and side surface of the permanent magnets 16, from
viewpoints of reducing magnetic leakage flux and suppressing axial
dislodgment of the permanent magnets 16.
Embodiment 4
[0091] FIG. 18 is a cross section that shows an embedded permanent
magnet rotary electric machine according to Embodiment 4 of the
present invention, FIG. 19 is an oblique projection that shows a
rotor core in the embedded permanent magnet rotary electric machine
according to Embodiment 4 of the present invention, and FIG. 20 is
a graph that shows a relationship between torque ripples and step
skew angle in the embedded permanent magnet rotary electric machine
according to Embodiment 4 of the present invention.
[0092] In FIGS. 18 and 19, an embedded permanent magnet rotary
electric machine 101 includes: an annular stator 1A; and a rotor 30
that is coaxially and rotatably disposed inside the stator 1A so as
to have an air gap 9 interposed.
[0093] The stator 1A includes: a stator core 2A that is produced by
stacking and integrating electromagnetic steel sheets, and that is
formed such that teeth 2b each protrude radially inward from an
inner wall surface of an annular back yoke 2a so as to be arranged
at a uniform angular pitch circumferentially; and a stator winding
3 that is mounted to the stator core 2A. In this case, twelve slots
2c that are formed by the back yoke 2a and adjacent teeth 2b are
arranged circumferentially. The stator winding 3 includes
concentrated winding coils 3a that are produced by winding
conductor wires onto each of the teeth 2b.
[0094] The rotor 30 includes: first and second rotor cores 121 and
122 that function as core segments that are produced by stacking
and integrating electromagnetic steel sheets, the first and second
rotor cores 121 and 122 having external shapes in which a plurality
of circular arc-shaped curved surfaces 13 are arranged at a uniform
angular pitch circumferentially and being disposed in an axial
direction so as to be coaxial; a rotating shaft 11 that is inserted
into and fixed to central axial positions of the first and second
rotor cores 121 and 122; and permanent magnets 16 that are embedded
into outer circumferential sides of the first and second rotor
cores 121 and 122.
[0095] The first and second rotor cores 121 and 122 are each
configured such that eight protruding portions that have a radius
of curvature R2, that are formed by the circular arc-shaped curved
surfaces 13, are arranged at a uniform angular pitch
circumferentially. Magnet housing apertures 15 are formed so as to
pass axially through the first and second rotor cores 121 and 122
on an inner radial side of each of the circular arc-shaped curved
surfaces 13. In addition, the permanent magnets 16 are inserted
into and fixed to each of the magnet housing apertures 15.
[0096] The first and second rotor cores 121 and 122 are fixed to
the rotating shaft 11 that is inserted into the central positions
thereof so as to be arranged coaxially in contact with each other
in the axial direction such that magnetic pole centers are offset
in a circumferential direction. Moreover, the first and second
rotor cores 121 and 122 are configured in a similar or identical
manner to the rotor core 12 in Embodiment 1 above except that eight
permanent magnets 16 are embedded, and the axial thickness is half.
Furthermore, a step skew angle is a circumferential angle between
the magnetic pole centers of the first and second rotor cores 121
and 122 that are arranged in the axial direction.
[0097] Generally, in embedded permanent magnet rotary electric
machines, if the stator windings are concentrated windings, then
harmonics are larger and torque ripples are more likely to increase
than when a stator winding that is made of distributed windings is
used. Harmonics are particularly large if there are eight poles and
twelve slots.
[0098] In this embedded permanent magnet rotary electric machine
101, because the first and second rotor cores 121 and 122 are
arranged coaxially in the axial direction such that magnetic pole
centers are offset in a circumferential direction, that is, a step
skew is applied, a shift arises in the phase of torque ripples that
are generated in the axial direction, enabling the torque ripples
to be reduced.
[0099] In eight-pole, twelve-slot motors, theoretically, if 1f is a
period in which the motor makes one revolution electrically, then
large torque ripples arise in a 6f component. Because of that, the
step skew is applied so as to set a phase difference of 30 degrees
electrically. Now, in the case of an eight-pole motor, 30
electrical degrees corresponds to 7.5 mechanical degrees. However,
because the permanent magnets 16 are embedded in the first and
second rotor cores 121 and 122, magnetic leakage flux arises that
flows axially through core portions of the first and second rotor
cores 121 and 122 that are positioned on an outer circumferential
side of the permanent magnets 16, making the phase shift in torque
ripples that forms in the axial direction different than the
theoretical 30 degrees.
[0100] Now, a relationship between the step skew angle (electrical
degrees) and torque ripples is shown in FIG. 20.
[0101] From FIG. 20, torque ripples become gradually smaller as the
step skew angle increases from 28 degrees, and torque ripples are
further reduced when the step skew angle is greater than or equal
to 30 degrees (mechanical angle: 7.5 degrees). Then, when the step
skew angle exceeds 43 degrees, reductions in torque ripples become
slow, and when the step skew angle exceeds 48 degrees, there is
hardly any reduction in torque ripples.
[0102] Since increasing torque ripples leads to decreases in
output, it is desirable to set the step skew angle to greater than
or equal to 30 electrical degrees and less than or equal to 48
degrees from the viewpoint of reducing torque ripples and
suppressing decreases in output. Here, a case in which there are
eight poles and twelve slots has been explained, but it has also
been possible to confirm that similar or identical effects can also
be achieved in three-phase motors in which the number of slots per
phase per pole in the motor is one half or one quarter.
Embodiment 5
[0103] FIG. 21 is a side elevation that shows a rotor core in an
embedded permanent magnet rotary electric machine according to
Embodiment 5 of the present invention.
[0104] In FIG. 21, first and second rotor cores 121 and 122 are
disposed coaxially such that magnetic pole centers are offset in a
circumferential direction so as to ensure a gap din an axial
direction.
[0105] Moreover, the rest of the configuration is formed in a
similar or identical manner to that of Embodiment 4 above.
[0106] In the rotor 30 according to Embodiment 4 above, because the
first and second rotor cores 121 and 122 are arranged so as to
contact each other in the axial direction, magnetic leakage flux
arises that flows axially through core portions of the first and
second rotor cores 121 and 122 that are positioned on an outer
circumferential side of the permanent magnets 16, leading to
decreases in output.
[0107] In the rotor 30A according to Embodiment 5, a gap d is
ensured between the first and second rotor cores 121 and 122 that
are arranged so as to line up in the axial direction. The amount of
magnetic leakage flux that flows axially through portions of the
first and second rotor cores 121 and 122 that are positioned on an
outer circumferential side of the permanent magnets 16 is thereby
reduced, enabling the step skew angle for reducing torque ripples
to be reduced. Output decreases when the step skew angle is
increased. Consequently, according to Embodiment 5, output can be
increased compared to Embodiment 4 above.
[0108] Now, it is possible to improve output by reducing the
magnetic leakage flux in the magnet magnetic flux if the gap d is
set to greater than or equal to the thickness B1 in core portions
of the first and second rotor cores 121 and 122 that are positioned
on an outer circumferential side of the permanent magnets 16, i.e.,
at the magnetic pole centers of the bridge portions 20. Thus, if t
is the sheet thickness of the electromagnetic steel sheets, it is
desirable to set the gap d such that d.gtoreq.0.4.times.t because
the manufacturable B1 is greater than or equal than
0.4.times.t.
Embodiment 6
[0109] FIG. 22 is a side elevation that shows a rotor core in an
embedded permanent magnet rotary electric machine according to
Embodiment 6 of the present invention.
[0110] In FIG. 22, a rotor core is constituted by first through
third rotor cores 13, 132, and 133 that function as core segments.
The first and third rotor cores 131 and 133 are configured so as to
be identical. The second rotor core 132 is configured in a similar
or identical manner to that of the first and third rotor cores 131
and 133 except that an axial length thereof is two times that of
the first and third rotor cores 131 and 133. The first through
third rotor cores 131 and 133 are arranged in an axial direction so
as to be coaxial at opposite ends of the second rotor core 132 so
as to be in contact therewith. The circumferential positions of the
magnetic pole centers of the first and third rotor cores 131 and
133 are aligned, and the magnetic pole centers of the second rotor
core 132 are offset in a circumferential direction from the
magnetic pole centers of the first and third rotor cores 131 and
133.
[0111] Moreover, the rest of the configuration is formed in a
similar or identical manner to that of Embodiment 4 above.
[0112] In Embodiment 6, the first and third rotor cores 131 and 133
are configured so as to be identical, and the circumferential
positions of the magnetic pole centers thereof are aligned.
Furthermore, the axial length of the first and third rotor cores
131 and 133 is half the axial length of the second rotor core 132.
The second rotor core 132 is step-skewed relative to the first and
third rotor cores 131 and 132. Thrust that acts in the axial
direction during rotation of the rotor 30B as a result of the
step-skewing is eliminated thereby. Consequently, loads on the
bearings of the embedded permanent magnet rotary electric machine
are reduced, enabling the occurrence of failure in the bearings to
be suppressed.
Embodiment 7
[0113] FIG. 23 is a partial enlargement that shows a vicinity of a
permanent magnet of a rotor in an embedded permanent magnet rotary
electric machine according to Embodiment 7 of the present
invention.
[0114] In FIG. 23, a rotor core 12B is configured such that a
distance Ln between facing magnet detent portions 18 is formed so
as to be greater than a thickness B2 at circumferential end
portions of bridge portions 20.
[0115] Moreover, the rest of the configuration is formed in a
similar or identical manner to that of Embodiment 1 above.
[0116] Magnetic flux that emerges from a first permanent magnet 16
flows through a magnetic path that passes through a core portion of
the rotor core 12B on an outer circumferential side between poles
toward a neighboring permanent magnet 16, and through a magnetic
path that passes through an interpolar core portion of the rotor
core 12B and returns to the first permanent magnet 16. The
magnitude of the amount of magnetic leakage flux in the magnetic
flux that emerges from the permanent magnets 16 is determined by
the thickness B2 at the circumferential end portions of the bridge
portions 20. Consequently, the amount of magnetic leakage flux does
not change even if Ln>B2. If Ln is increased, the mechanical
strength of the bridge portions 20 also increases so as to be able
to withstand high-speed rotation.
[0117] According to Embodiment 7, because Ln is greater than B2,
resistance to centrifugal forces can be increased without
increasing the magnetic leakage flux.
[0118] Moreover, in each of the above embodiments, a single long
permanent magnet is housed in each of the magnet housing apertures,
but a plurality of short permanent magnets may be housed in each of
the magnet housing apertures so as to line up in a single
column.
EXPLANATION OF NUMBERING
[0119] 1, 1A STATOR; 9 AIR GAP; 10, 10A, 10B, 30, 30A, 30B ROTOR;
11 ROTATING SHAFT; 12, 12A, 12B ROTOR CORE; 13 CIRCULAR ARC-SHAPED
CURVED SURFACE; 14 CYLINDRICAL SURFACE; 15, 15A MAGNET HOUSING
APERTURE; 16, 16A PERMANENT MAGNET; 17 AIR GAP PORTION; 20 BRIDGE
PORTION; 21 END PLATE; 121 FIRST ROTOR CORE (CORE SEGMENT); 122
SECOND ROTOR CORE (CORE SEGMENT); 131 FIRST ROTOR CORE (CORE
SEGMENT); 132 SECOND ROTOR CORE (CORE SEGMENT); 131 THIRD ROTOR
CORE (CORE SEGMENT); d GAP.
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